Purification of partially fluorinated cyclobutanes

ABSTRACT

Methyl formate, ethyl formate and propylene oxide are used as entraining agents to separate close-boiling mixtures of partially fluorinated cyclobutanes.

United States Patent 1191 1111 3,850,759 Hutchinson Nov. 26, 1974PURIFICATION OF PARTIALLY 3,345,420 10/1967 GGICh 260/648 r 3,391,2017/1968 Jaeger 203/58 FLUORINATED CYCLOBUTANES 3,409,512 11/1968 Anelloet a1. 203/60 Inventor: am c nson, 36 SE. 3,449,218 6/1969 Jaeger 203/53Woodland Rd., Bartlesville, Okla.

74003 Przmary Exammer-W11bur L. Bascomb, Jr. [22] F11ed: Oct. 23, 1973Attorney, Agent, or FirmNeuman, Williams, 21 Appl. No.1 408,481 Anderson[52] U.S. Cl. 203/58, 203/60, 260/648 F 57 S CT [51] Int. Cl B0ld 3/36,C07c 23/06 [58] Field of Search 260/648 F; 203/58, 60 Methyl formate,ethyl formate and propylene oxide are used as entraining agents toseparate close-boiling [56] References Cited mixtures of partiallyfluorinated cyclobutanes, UNITED STATES PATENTS 4 Cl N D 2,384,4499/1945 Benning et 11. 260/648 F 0 raw'ngs PURIFICATION OF PARTIALLYFLUORINATED CYCLOBUTANES This invention relates to the separation offluorinated hydrocarbons and particularly to the separation offluorinated hydrocarbons having the same carbon skeleton but differingfrom one another in the relative numbers or position of hydrogen andfluorine atoms present in the molecule.

It is known that reaction between ethylene and tetrafluoroethylene canbe effected to form 1,l,2,2-tetrafluorocyclobutane. Fluorination of thesaid tetrafluorocyclobutane yields octafluorocyclobutane as the ultimateproduct. However, there is also produced incompletely fluorinatedcyclobutanes such as 1,1,22,3- pentafluorocyclobutane, l ,1,2,2,3,3-hexafluorocyclobutane, trans-l ,1 ,2,2,3,3,4-hexafluorocyclobutane, heptafluorocyclobutane and cis- 1 ,1,2,2,3,4-hexafluorocyclobutane. The fluorination mixtures can besubjected to fractional distillation to separate as relatively purecompounds a number of the components in the reaction mixture. Thus, forexample, octafluorocyclobutane (B.P. 6 C.), heptafluorocyclobutane (B.P.17 C.) and cis-1,l ,2,2,3,4-hexafluorocyclobutane (B.P. 63 C.) can bereadily separated by fractional distillation. However, certain materialshave very close boiling points which prevent separation by straightfractional distillation. Thus, l,l,2,2,3,3-hexafluorocyclobutane has aboiling point of 26 C. while trans- 1,1,2,2,3,4-hexafluorocyclobutanehas a boiling point of 27 C. Similarly, l,1,2,Z-tetrafluorocyclobutanehas a boiling point of 50 C. while l,l,2,2,3-pentafluorocyclobutane hasa boiling point of 51 C.

It is an object of this invention to provide a method for the separationof pentafluorocyclobutane and tetrafluorocyclobutane mixtures byazeotropic distillation.

Another object of this invention is to provide a method for theseparation of trans-l,1,2,2,3,4-hexafluorocyclobutane and 1,1,2,2,3,3-hexafluorocyclobutane by azeotropic distillation.

A further object of this invention is to, provide entraining agents forazeotropic distillation of mixtures of pentafluorocyclobutane andtetrafluorocyclobutane as well as mixtures of trans-l,l,2,2,3,4hexafluorocyclobutane and 1,l,2,2,3 ,3-hexafluorocyclobutane.

Other objects and advantages will become apparent from the followingdescription of the invention.

1 have discovered that pentafluorocyclobutane and tetrafluorocyclobutanecan be effectively separated by fractional distillation by adding ethylformate to the mixture prior to distillation. I have discovered furtherthat l,1,2,2,3,3-hexafluorocyclobutane andtransl,l,2,2,3,4-hexafluorocyclobutane can be effectively separated byfractional distillation by adding methyl formate or propylene oxide tothe mixture prior to distillation.

In accordance with one embodiment of this invention, a mixture of1,1,2,2-tetrafluorocyclobutane and 1,l,2,2,3-pentafluorocyclobutane issubjected to azeotropic distillation using ethyl formate as anentraining agent. The minimum proportions of entraining agent is 1.7lb./lb. l,l,2,2,3-pentafluorocyclobutane plus 0.1 lb./lb.1,l,2,Z-tetrafluorocyclobutane. Excess entrainer did not appearbeneficial. An azeotrope containing about weight percent ethyl formatein tetrafluorocy clobutane boils at a temperature of about 502 C. at

745 millimeters pressure. Pentafluorocyclobutane remains in the kettle.The ethyl formate entraining agent can be separated from overhead orkettle product by extraction with cold sulfuric acid percent). Incarrying out the azeotropic distillation, rectification improves theefficiency and reflux ratios of about 5:1 with a 50 plate column toabout 50:1 with a 5 plate column are preferred. 1

In accordance with a second embodiment of the invention, a mixture of1,1,2,2,3,3-hexafluorocyclobutane andtrans-1,1,2,2,3,4-hexafliuorocyclobutane is subjected to azeotropicdistillation using methyl formate as an entraining agent. The entrainingagent is employed in amounts from about 0.5 to 10, preferably l to 3,parts per part by weight of the mixture. The 1,1,-2,2,3-hexafluorocyclobutane fon'ns an azeotrope with methyl formatecontaining 70 weight percent of the former and 30 weight percent of thelatter, which boils at a temperature of about 27 C. at 744 millimeterspressure. The methyl formate can be separated from overhead or kettleproducts simply by washing with water.

In accordance with a third embodiment of the invention, a mixture of1,1,2,2,3,3-hexafluorocyclobutane andtrans-1,1,2,2,3,4-hexafluorocyclobutane is subje'cted to azeotropicdistillation using propylene oxide as an entraining agent. Theentraining agent is employed in amounts of about 1.0 to 10, preferably 2to 5, parts per part by weight of the mixture. The azeotrope boils atabout 30 C. at 744 millimeters of mercury and contains about 31 weightpercent 1,] ,2,2,3,3- hexafluorocyclobutane and 69 weight percent of thetrans compound. The trans-l,1,2.2,3,4-hexafluorocyclobutane remains inthe kettle. The propylene oxide can be separated from overhead or kettleproducts by washing with water. g

The following examples are given to further illustrate the invention.

EXAMPLE I 429 grams of a mixture comprising approximately 92 peak heightpercent of l,1-,2,2-tetrafluorocyclobutane (C H F and 8 peak heightpercent of 1,1 ,2,2,3-pentafluorocyclobutane (C H F werechar'ged to astill, together with 39 grams of ethyl formate. The still used compriseda 3 foot X inch diameter column with silvered vacuum jacket and packedwith Heli-Pak (No. 3014, Hastelloy B; 0.030 inch X 0.070 inch X 0.070inch). The automatic take-oh head was water cooled and delivered into agraduated receiver. The kettle was an insulated, 500 cubic centimeterround bottom flask heated by a mantle controlled by a Powerstat. Refluratios of from 20:1 to :1 were employed.

Data from this fractionation are recorded in Table I. The analyses wereperformed with a Carle Basic Gas Liquid Chromatographer using a 5 foot Xinch Carbowax 20M column at 70 C. The recording potentiometer had notintegrator. The CarleGas Liquid Chromatographer has a thermistordetector. Small cuts were usually taken and immediately analyzed by gasliquid chromatography (GLC). The chromatograms obtained with the CarleBasic Gas Chromatographer were evaluated by height of the peaks(labelled Peak Height percent). Compositions (weight percentages of eachcomponent) were obtained by dividing the peak heightsby the factors0.85, 1.08 and 1.00, respectively, for the componentspentafluorocyclobutane, ethyl formate 3 4 and tetrafluorocyelobutane andthen normalizing the separated from C H F by azeotropie distillationusing resulting figures to 100 weight percent. ethyl fomiate asentramer. Separation of the two com- TABLE 1 Overhead Product CumulativeGLC Analysis Peak Height "/1 Cut Overhead Temp. C. Overhead Overhead.Wt. "/r Ethyl No. At 744 mm Press. gms. gms. Distilled Lights* C H F (111 1), Formate In Dry Ice Trap 2.4 35.8

Shut Down Overnight 9 45.2/485 9.5 45.3 8.4 10.6 76.0 0.0 13.4 1048.2/49.4 6.3 51.6 9.6 5.0 82.0 1.6 11.4 11 49.4/495 1.4 53.0 9.9 0.583.6 2.4 13.5 12 48.5/49.0 1.0 54.0 10.1 2.7 82.6 2 0 12.7 Shut down toadd 39 grams Ethyl Formate which was being depleted 13 48.5/47.1 2.856.8 10.6 2.4 86.2 0.3 11.1 14 47.1/47.8 3.2 60.0 11.2 2.0 87.6 0.3 10.615 47.8/48.2 4.1 64.1 11.9 2.4 85.3 0.6 11.7 16 482/490 3.2 67.3 12.50.7 83.4 0.3 15.6 Shut Down Overnight Barometric Pressure 745.2 mm. Hg.17 48.2/487 3.1 70.4 13.1 0.7 85.2 0.7 13.4 18 485/490 2.1 72.5 13.5 0.286.2 1.0 12.6 19 48.8/49.6 3.7 76.2 14.2 0.6 87.7 1.2 11.5 20 496/5005.3 81.5 15.2 0.3 85.3 1.5 12.9 21 50.0/50.0 2 3 83.8 15.6 0.0 83.2 1.615.2

Shut Down Overn' ht 22 50.0/50.1 6.5 90.3 16.8 0.0 81.6 2.1 15.2 2350.1/50.1 9.9 100.2 18.7 24 50.1/50.1 9.5 109.7 20.4 0.1 83.2 0.1 16.6

Shut Down Overnight 25 50.1/50.1 40.5 150.2 28.0 26 50.1/50.2 18.5 168.731.4

Shut Down Over Weekend Barometric Pressure 743.8 mm. Hg. 27 50.1/50.239.5 208.2 38.9 28 50.2/50.2 35.2 243.4 45.3 0.0 85.2 0.4 14.4

Shut Down Overnight Barometric Pressure 744.4 mm. Hg. 29 50.2/50.2 59.4302.8 56.5 0.0 86.4 0.1 13.5

Shut Down Overnight Barometric Pressure 747.8 mm. Hg. 30 505/505 10.4313.2 58.4 0.0 74.8 3.4 21.8 31 505/505 40.0 350.2 65.4 0.0 74.3 4.521.2

Shut Down Overnight Barometric Pressure 751.6 mm. Hg. 32 506/506 19.7369.9 68.9 0.0 73.7 3.7 22.6 Shut Down Overnight Barometric Pressure747.2 mm. Hg. 33 50.5/50.7 39.4 409.3 76.3 0.0 69.8 3.6 26.6

Shut Down Overnight Barometric Pressure 740.0 mm. Hg.

34 50.7/51.5 22.3 431.6 80.5 0.0 51.2 6.7 42.1 35 51.2/52.0 6.3 437.981.6 0.0 46.7 14.0 39.3 Shut Down Overnight Barometric Pressure 740.4mm. Hg.

Kettle Residue 80.0 536.0 100.0 0.0 0.08 31.0 68.7

Lost 30.0

' l.12.2.3.3-hexafluomcyelohutune and trans-l .l2.2.3.4-hexafluoroeyclobutune The azeotropic composition was evidencedby cuts pounds by ordinary distillation without an entrainer 21 through29 wherein lights were absent in the was found to be impossible.overhead product and the amount of pentafluoroey- EXAMPLE n clobutanewas neghgible. Composition of the azeotrope milliliters of a mixturecomprising approximately was determined from the peak heights to beabout 15 60 peak height percent of 1 1 2 2 3 3 hexafluomcywelghtpercemethyl formate and welghtpercem 1v 6 clobutane (herein calledii-tiii 2111640 peak height 1,2,2-tetrafluorocyclobutane. The azeotropeboiled at percent of 12 2 3 4 h fl l b t about 502 C. at 745 millimetersof mercury pressure (h erein called trans) were char ed to a still toether Cuts 21 through 29 also Illustrate that 4 4 4 can be with 9.6milliliters of methyl fo rmate. The still comprised a concentric tubecolumn (about 13 inches long, about millimeters internal diameter;silvered vacuum jacket; rated 40 plates at 80 cubic centimeters per hourboil-up rate), a vacuum jacketed head with triagcuts 5 through 8 whereinthe azeotrope boiled at about 27 C. at 744 millimeters of mercurypressure and contained about 70 weight percent of the 1H. 1 H compoundand 30 weight percentmethyl formate.

netic takeoff and fitted with a thermocouple read by 5 a potentiometerto 02 C., a conical, graduated receiver and a 25 milliliter conicalkettle heated by a EXAMPLE m mantle and wrapped in glass wool. Thecondenser was 4.6 milliliters of a mixture comprising approximately acold-finger type cooled by dry icelfluorotflc o e- 50 area percent ofl,1,2,2,3,3-hexafluorocyclobutane thane. The receiver was cooled withice when distilling l0 (herein called lH,lH), and 50 area percent oftransthe hexafluorocyclobutane. A reflux ratio of 20:1 wasl,1,2,2,3,4-hexafluorocyclobutane (herein called employed. trans) werecharged to a still together with 12.0 millili- Data from thefractionation are recorded in Table I1. ters of propylene oxide. Thestill used comprised a con- The analyses were performed with a CarleBasic Gas centric tube column (about 13 inches long, about 10Chromatographer using a 5 foot X /8 inch Carbowax millimeters internaldiameter; silvered vacuum jacket; M column at 70 C. The recordingpotentiometer rated plates at 80 cubic centimeters per hour boil-up hadno integrator. The Carle Basic Gas Chromatograrate), a vacuum jacketedhead with magnetic take off pher Chromatographer had a thermistordetector. and fitted with a thermocouple read by a potentiometer Smallcuts were usually taken and immediately anato 02 C., a conical,graduated receiver and a 25 millilyzed by gas liquid chromatography(GLC). The chro- 20 liter conical kettle heated by a mantle and wrappedin matograms obtained with the Carle Basic Gas Chromaglass wool. Thecondenser was a cold-finger type tographer Chromatographer wereevaluated by height cooled by dry ice/fluorotrichloromethane. Thereceiver of the peaks (labelled Peak Height percent). Peak was cooledwith ice when distilling the hexafluorocyheights were converted tocompositions, weight perclobutane. A reflux ratio of 20:1 was employed.cent, by dividing by the factors 1.00 for trans, 1.65 for 25 Data fromthe fractionation are recorded in Table III. 1H,1H, and 1.13 for methylformate and then normaliz- The analyses were performed with an Aerograph1520 ing to 100 weight percent. fitted with atris-(2-cyanoethoxy)propane column at TABLE II Overhead ProductCumulative Volume GLC. Peak Height Cut Overhead Temp. C. OverheadOverhead Volume Methyl No. At 744.4 mm. Hg. Vol.. ml. ml. DistilledCJHF7 1H. 1H Trans Formate .1 l7.0/18.8 0.2 0.2 1.8 46 47 2 5 218.8/22.0 0.3 0.5 4.4 35.1 58.0 1.9 5.0 3 220/240 0.2 0.7 6.1 25 66 2 74 240/260 0.3 1.0 8.8 20.8 65.3 2.4 1 1.5 5 26.0/26.6 0.2 1.2 11.1 9.464.9 7.5 18.2 6 26.6/26.6 0.2 1.4 13.3 6.5 72.2 0.4 20.9 7 26.6/26.6 0.21.6 14.0 5.1 69.4 3.0 22.5 8 26.6/27.4 0.2 1.8 15.8 3.9 66.3 5.3 24.5 9274/274 0.2 2.0 17.5 3.2 64.7 6.5 25.6 10 27.4/294 0.8 2.8 24.6 1.6 52.613.8 32.0 11 29.4/29.2 0.1 2.9 25.4 0.2 30.3 23.5 46.0 12 292/292 0.33.2 28.1 0.0 22.1 29.4 48.5 13 292/294 0.3 r 3.5 30.8 0.0 22.1 29.4 48.514 29.4/29.6- 0.2 3.7 32.6 0.0 13.6 32.4 54.0 15 29.6/30.0 0.3 4.0 35.20.0 9.7 33.7 56.7 Kettle Residue 7.4 l 1.4 1 0.0 0.0 19.0 81.0

' Lost 2.4

Inspection of the peak height data (related to compo- 50 C. and apotentiometer having 21 Disc integrator.

sition as previously explained) in Table 11 indicates that it ispossible to separate 1H,1H from trans by azeotropic distillation usingmethyl formate as entrainer. Cut 1 contained little of the transcomponent whereas The chromatograms from the Aerograph were evaluated bypeak area and are labelled area percent". Compositions in weightpercentages were obtained from the peak areas by dividing the areas bythe factor the kettle residue contained no 1H.1H. Separation of 1.00 forboth trans and lH,1H and by the factor 2.00

these two components by ordinary distillation was not possible. Theazeotropic composition was evidenced by for propylene oxide andnormalizing to weight percent.

TABLE III Overhead Product Cumulatlve Volume GLC. Area 76 Cut OverheadTemp. C. Overhead Overhead Volume Propylene No. At 743.8 mm. Hg. Vol..ml. ml. Distilled C HF 1H, 1H Trans Oxide 4 312/312 0.3 1.00 (1.0 ll.l31.3 0.00 57.5

TABLE 111 ntinued Overhead Product Cumulative Volume GLC, Area '71 CutOverhead Temp. C. Overhead Overhead Volume Propylene No. At 743.8 mm.Hg. Vo|.. ml. ml. Distilled C,HF 1H, 1H Trans Oxide 5 31.2/3l.4 0.2 1.27.2 8.1 31. 0.1 60.6 6 3l.4/3l.8 0.3 1.5 9.0 6.7 30.8 0.2 62.3 73l.8/32.0 0.3 1.8 10.8 4.7 29.4 0.1 65.8 8 32.0/32.0 0.6 2.4 14.5 1.927. 0.2 70.0 9 320/320 0.4 2.8 16.9

Shut Down Overnight Barometric Pressure 744.4 mm. Hg.

Inspection of the data of Table 111 indicates that it was possible todistill 1H,lH overhead almost free of the trans component in thepresence of propylene oxide as entrainer. The azeotropic composition wasevidenced by cuts 12 through 15 wherein the azeotrope boiled at atemperature of about 326 C. at a pressure of 744 millimeters of mercuryand contained about 69 weight percent propylene oxide and 31 weightpercent of the 111,111 component.

Those modifications and equivalents which fall within the spirit of theinvention are to be considered a part thereof.

What is claimed is:

l. A process of separating a close-boiling mixture of partiallyfluorinated cyclobutanes containing 4 to 6 fluorine atoms whichcomprises subjecting said mixture to UNITED STATES PATENT oFFlcEQERTIFICATE OF CORRECTION Patent No. 3,850,759 Dated November 26, 974

Inventor(s) William M. Hutchinson It is certified that error appears inthe above-identified patent and that said Letters Patent are herebycorrected as shown below:

Column 1, line 17, "trans-1,1,2,2,3,3,4-hexafluorocyclobutane" should betransl,1,2,2,3,4-hexafluorocyclobutane Column 2, line 59, not should beno line 60, "has" should be had Column 5, lines 14 & l5, "Carle BasicGas Chromatographer" should be Carle Basic gas chromatograph lines 17 &l8, 'Carle Basic Gas Chromatographer Chromatographer" should be Carle-Basic gas chromatograph lines 21 & 22, "Carle Basic Gas ChromatographerChromatographer" should be Carle Basic gas chromatograph Signed andSealed this twenty-sixth Day of August 1975 [SEAL] Arrest:

RUTH C. MASON Arlesting Officer C MARSHALL DANN (ummisxiuncr uj'lalcnlsand Trademarks

1. A PROCESS OF SEPARATING A CLOSE-BOILING MIXTURE OF PARTIALLYFLUORINATED CYCLOBUTANES CONTAINING 4 TO 6 FLUORINE ATOMS WHICHCOMPRISES SUBJECTING SAID MIXTURE TO OZEOTROPIC DISTILLATION IN THEPRESENCE OF AN ENTRAINING AGENT SELECTED FROM THE GROUP CONSISTING OFMETHYL FORMATE, ETHYL FORMATE AND PROPYLENE OXIDE.
 2. A process inaccordance with claim 1 wherein the close-boiling mixture is1,1,2,2-tetrafluorocyclobutane and 1,1,2,2,3-pentafluorocyclobutane andwherein the entraining agent is ethyl formate.
 3. A process inaccordance with claim 1 wherein the close-boiling mixture is1,1,2,2,3,3-hexafluorocyclobutane and trans-1,1,2,2,3,4-hexafluorocyclobutane and the entraining agent is methylformate.
 4. A process in accordance with claim 1 wherein theclose-boiling mixture is 1,1,2,2,3,3-hexafluorocyclobutane and trans-1,1,2,2,3,4-hexafluorocyclobutane and the entraining agent is propyleneoxide.